1. Field of the Invention
The present invention relates to a power supply assembly for a vehicle having two power supply systems, namely a high-voltage storage cell and a low-voltage storage cell.
2. Description of the Related Art
FIG. 3 is a block diagram showing a conventional power supply assembly for a vehicle.
In FIG. 3, a reference numeral 1 denotes an engine for moving an automobile, a reference numeral 2 denotes a generator connected to and driven by the engine 1; a reference numeral 3 denotes a starter motor for starting the engine 1, a reference numeral 4 denotes an electrical load, constituted by a radio, lamps, etc., a reference numeral 5 denotes a storage cell to which the output voltage of the generator 2 is applied, a reference numeral 6 denotes a key switch, and a reference numeral 7 denotes a controller for monitoring the terminal voltage of the storage cell 5 and regulating the output voltage of the generator 2 based on the terminal voltage of the storage cell 5.
In a conventional power supply assembly for a vehicle constructed in the above manner, when the key switch 6 is closed, closing a starter motor drive switch 9, the voltage of the storage cell 5 is applied to the starter motor 3, current flows though the motor portion of the starter motor 3, and the starter motor 3 begins to rotate. The engine 1 is driven thereby. Then, the generator 2 is driven by the engine 1 and starts to generate power. The output voltage of the generator 2 is regulated, at 14.4 V, for example, and applied to the storage cell 5, serving to recharge the storage cell 5.
When a switch 8 is closed, the terminal voltage of the storage cell 5 is applied to the desired electrical load 4, operating the desired electrical load 4.
Now, the storage cell 5 is depleted by the use of the starter motor 3 and the electrical load 4, decreasing the terminal voltage thereof.
Thus, the controller 7 monitors the terminal voltage of the storage cell 5 and provides ON/OFF control of the excitation current of the generator 2 in response to the terminal voltage, regulating the charging of the storage cell 5.
As indicated above, in the conventional power supply assembly for a vehicle, only one storage cell 5 is mounted, and furthermore, because the storage cell 5 is connected to ground even when the engine 1 is at rest, minute currents flow when the engine is stopped, causing the storage cell 5 to discharge. Furthermore, in a vehicle adopting an idling-stop-and-start system, frequent use is made of the starter motor 3, rapidly depleting the storage cell 5. Thus, one problem has been that the terminal voltage of the storage cell 5 has been reduced by such discharging and rapid depletion, making it impossible to drive the starter motor 3, and therefore to start the engine 1.
In such cases, it is necessary to start the engine by means of the assistance of another vehicle, giving rise to extremely inconvenient situations.